This invention relates to a double-head automatic grinding machine.
When a hard and brittle workpiece, with sufficient margin for grinding is ground, the axis of one diamond cup-shaped grinding wheel can be positioned offset from the center axis of the workpiece by the distance corresponding to the effective radius (the distance from the axis of the wheel to one half of the wall thickness of the wheel) of the cutting end face of the grinding wheel. In this case the effective radius of the cutting end face of the grinding wheel is positioned in a position tangent to the outer periphery of the work and the work is ground with the rotation of the work and the feeding movement of the table maintained at a low speed. This results in spiral feed pitches being formed on the outer periphery of the work whereby coarse, medium and fine grinding stages can be effectively and simultaneously performed on the work. However, when the work is a crystal material (such as glass, quartz, ceramic or silicone), fine cracks tend to develop in the work outer periphery. Thus, in order to remove such cracks from the work surface, medium and fine grinding stages are further required. If the workpiece is a super hard metal, portions of the workpiece tend to break off to thereby make the grinding in a single stage difficult. The grinding operation has to be divided into a number of stages, the last of the stages or the fine grinding then has to be performed by a grinding wheel different from the grinding wheel employed in the preceding grinding stages.